1. Field of the Invention
The present invention relates to a lead frame and, in particular, to a lead frame that deterioration in characteristics thereof can be suppressed even after long-term use, a method of making the lead frame and a light receiving/emitting device using the lead frame.
2. Related Art
A lead frame used for a conventional semiconductor device is known in which a silver coating as a reflection region is formed on an outermost layer at a portion of a region surrounded by an enclosure (or reflector) and a gold or gold alloy coating is formed on an outermost layer at a region except the silver coating (e.g., Japanese patent No. 3940124). When the lead frame in Japanese patent No. 3940124 is used for mounting, e.g., a light-emitting device thereon, light emitted from the light-emitting device toward the lead frame can be efficiently reflected on the region with the silver coating to enhance the emission efficiency.
However, when the silver coating of the lead frame in Japanese patent No. 3940124 is exposed outside before mounting the light emitting device, a problem may arise that the reflectivity of the silver lowers due to sulfuration and/or oxidation. Furthermore, a problem may arise that, even when the inside of the enclosure is filled by a sealing resin after mounting the light-emitting device, the silver coating is sulfurated and/or oxidized by sulfur and/or oxygen penetrated through the resin due to long-term use (e.g., about one year use), so that the reflectivity of the silver coating significantly lowers.